Enantioselective Synthesis of 4, 5-Dihydropyrroles via Domino Ring

Feb 7, 2013 - Enantioselective Synthesis of 4,5-Dihydropyrroles via Domino Ring-Opening Cyclization (DROC) of N-Activated Aziridines with Malononitril...
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Enantioselective Synthesis of 4,5-Dihydropyrroles via Domino RingOpening Cyclization (DROC) of N‑Activated Aziridines with Malononitrile Manas K. Ghorai* and Deo Prakash Tiwari Department of Chemistry, Indian Institute of Technology, Kanpur 208016, India S Supporting Information *

ABSTRACT: An efficient and practical strategy for the synthesis of highly functionalized racemic and non-racemic 4,5-dihydropyrroles via domino ring-opening cyclization (DROC) of activated aziridines with malononitrile in excellent yield and stereoselectivity is described. The reaction serves as a tool for the synthesis of a large variety of substituted 4,5dihydropyrroles in enantiomerically pure forms.

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INTRODUCTION Dihydropyrroles are an important class of heterocyclic compounds found as a functional core of various natural products and pharmaceutical agents.1 Moreover, some of them serve as excellent precursors for various nitrogen-containing heterocyclic compounds of synthetic and biological interest.2 A number of attractive routes have been designed for the synthesis of these heterocycles.3 Although many efforts have been devoted for the synthesis of 2,5- and 2,3-dihydropyrroles,3 comparatively less attention has been paid to 4,5-dihydropyrroles4 despite their numerous applications in natural product chemistry1a,c,2a and spin trapping experiments.5 Aziridines6−8 have been utilized as one of the most suitable building blocks for the synthesis of various nitrogen containing heterocyclic compounds.7 Surprisingly, they have been less explored for the synthesis of substituted dihydropyrroles.9,10 To the best of our knowledge there is no report for the synthesis of enantiomerically pure 4,5-dihydropyrroles from aziridines. Over the years, we have been involved in SN2-type ring-opening followed by alkylative cyclization of chiral aziridines8 for the synthesis of enantioenriched targets of contemporary interest.8a,c−h We realized that chiral substituted 4,5-dihydropyrroles could easily be synthesized via ring-opening followed by cyclization of chiral aziridines with malononitrile in a domino fashion. We have developed a simple and highly efficient strategy for the stereoselective synthesis of 4,5-dihydropyrroles with a synthetically important enaminonitrile moiety11 via a Lewis acid (LA) catalyzed domino ring-opening cyclization (DROC) of substituted aziridines with malononitrile for the first time (Scheme 1). Herein, we present our results in detail.

Scheme 1. Stereoselective Synthesis of 4,5-Dihydropyrroles via DROC of Aziridines with Malononitrile

Table 1. Optimization Study

conditions

temp

time (h)

yielda (%)

1 2 3 4 5 6 7 8 9 10

NaH, THF NaH, THF NaH, Cu(OTf)2,b THF NaH, Sc(OTf)3,b THF NaH, Yb(OTf)3,b THF NaH, Zn(OTf)2,b THF NaH, Ti(OiPr)4,b THF t-BuOK, Sc(OTf)3,b THF t-BuOK, Sc(OTf)3,b THF t-BuOK, THF

RT RT−60 °C RT−60 °C RT−60 °C RT−60 °C RT−60 °C RT−60 °C RT−60 °C RT RT−60 °C

4.5 2.5 1.0 0.5 1.0 1.75 1.25 0.5 1.5 2.0

39 42 58 94 86 86 77 97 97 45

a

Yields after column chromatographic purification. b20 mol % of LA catalyst was used.

reaction (4.5 h), the corresponding 4,5-dihydropyrrole 3a was obtained in 39% yield. In another set of experiments, when the reaction mixture was heated at 60 °C, the starting material was

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RESULTS AND DISCUSSION Initially, we carried out a reaction of 2-phenyl-N-tosylaziridine 1a with 1.5 equiv of malononitrile 2 using NaH as the base in THF at room temperature (Table 1), and after completion of the © XXXX American Chemical Society

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Received: December 28, 2012

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dihydropyrroles in excellent yields (entry 2−5). It is needless to mention that a fluoro substituent on the aromatic ring had found numerous applications in the pharmaceutical industry.14 Interestingly, when 1n was reacted with malononitrile under optimized reaction condition, the corresponding deacetylated product 3n was obtained probably due to LA catalyzed hydrolysis of the acetyl group under the reaction condition. To broaden the scope of our protocol, it was extended further for the synthesis of chiral 4,5-dihydropyrroles. For this purpose enantiomerically pure alkyl (isopropyl, benzyl, methyl, etc.) substituted aziridines (S)-1d,o,p and 2-phenyl-N-nosylaziridine (R)-1g were employed as the substrates (Table 4). The DROC of chiral aziridines (S)-1d,o,p with malononitrile produced the corresponding dihydropyroles in enantiomerically pure forms as a single regioisomer (Table 4). Similarly, when chiral 2-phenylN-nosylaziridine (R)-1g was used as the substrate, the corresponding dihydropyrrole (R)-3g was obtained in enantiomerically pure form (entry 5). The strategy was further extended to 2,3-disubstituted chiral aziridines7b to obtain highly substituted chiral 4,5-dihydropyrroles (Table 5). When trans-2-phenyl-3-n-propyl-N-tosylaziridine (2S,3S)-1q was reacted with malononitrile, the corresponding cis-dihydropyrrole (4S,5S)-3q was obtained in quantitative yield as a single diastereomer. A similar result was obtained with (2S,3S)-1r as the substrate, and the corresponding product (4S,5S)-3r was produced in diastereomerically pure form with quantitative yield. The cis-stereochemistry of the products 3r−s were determined by NOE experiments.15 In the compound 3r the allylic protons Ha and Hb showed NOE enahancement with the aromatic ortho proton (Hortho), whereas there was no such NOE relation of Hd (benzylic proton) with Ha and/or Hb, confirming the cis relationship of the phenyl and allyl groups (Figure 1). With a view to synthesizing highly functionalized dihydropyrroles suitable for further synthetic manipulations into various other motifs, we studied the DROC of trans aziridine 1s with malononitrile. As expected, the product 3s was obtained in excellent yield as a single diastereomer with 4,5-cis appendages. Compound 3s can be transformed into various other functional groups via functional group interconversion of the TBS ether group (Scheme 2). We believe that the reaction follows an SN2-type pathway as proposed by us earlier.8 The LA activated aziridine intermediate (A) undergoes nucleophilic attack by malononitrile anion to generate another intermediate B, which upon intramolecular cyclization and quenching by aqueous NH4Cl followed by tautomerization provides the dihydropyrrole products 3 (Scheme 3). For wider applicability of the developed strategy as a general methodology, the dihydropyrrole 3g was denosylated6l,8a to the corresponding N-unsubstituted product 415 following literature reports (Scheme 4).

fully consumed in 2.5 h without any appreciable improvement in the yield of 3a. To find out the optimum reaction conditions (shorter reaction time and maximum yield), various Lewis acid catalysts and bases were screened for the DROC of 1a with 2, and the results are shown in Table 1. The best result was obtained using Sc(OTf)3 as the LA and t-BuOK as the base; 3a was produced in 97% yield (Table 1, entry 8). Having the optimized reaction condition in hand, we intended to apply our protocol for the synthesis of various substituted 4,5-dihydropyrroles (Table 2). The product Table 2. Scope of the Reaction with various Monosubstituted N-Sulfonyl Aziridines

entry

aziridine

product(s)

yielda (%)

1 2 3 4 5 6

1a: R1 = C6H5, R2 = H, R3 = 4-MeC6H4 1b: R1 = 3-ClC6H4, R2 = H, R3 = 4-MeC6H4 1c: R1 = C6H5, R2 = H, R3 = 4-t-BuC6H4 1d: R1 = iPr, R2 = H, R3 = 4-MeC6H4 1e: R1 = n-Oct, R2 = H, R3 = 4-MeC6H4 1f: R1 = R2 = -(CH2)4, R3 = 4-MeC6H4

3a + 3a′ 3b + 3b′ 3c + 3c′ 3d 3e 3f

97b,c 90b,d >99b,e 92 99 75

a

Yields of isolated products after column chromatographic purification. bCombined yields of both the regioisomers. c3a:3a′ 8:1. d3b:3b′ 3:1. e3c:3c′ 5:1 (determined from 1H NMR of the crude reaction mixture).

3a was obtained as a mixture of regioisomers (3a and 3a′) with high regioisomeric ratio (8:1) (entry 1). Similar DROC of aziridines 1b and 1c with 2 produced the corresponding dihydropyrroles 3b (along with 3b′) and 3c (along with 3c′), respectively, in excellent yields (entry 2, Table 2). Formation of the minor regioisomer is probably due to the partial attack of the malononitrile at the less substituted position of aziridines 1a−c. When alkyl aziridines 1d,e were used as the substrates, the corresponding 4,5-dihydropyroles 3d,e were obtained in excellent yields as a single regioisomer via the attack of the nucleophile at the less sterically hindered position of the aziridines (entry 4 and 5). Compounds of the type 3e possessing a hydrophilic head (-NH2 group) and a hydrophobic tail are of both industrial (surfactants) and biological (lipid bilayer of cell membranes) importance. The DROC of cyclohexene aziridine 1f with malononitrile was found to be extremely efficient, and the corresponding fused 4,5-dihydropyrrole 3f was obtained as a single diastereomer. To the best of our knowledge, this is the first report for the synthesis of fused dihydropyrrole with synthetically explorable enamino-nitrile functionality. Since N-nosylaziridines are more reactive than N-tosylaziridines and also the nosyl group is easily removable,12 we explored DROC of 2-aryl-N-nosylaziridines with malononitrile 2. When 2phenyl-N-nosylaziridine 1g was reacted with malononitrile, the corresponding dihydropyrole 3g was obtained in excellent yield as a single regioisomer after column chromatographic purification.13 Encouraged by this result, a number of substituted 2-aryl-N-nosylaziridines were studied for DROC with malononitrile, and in all the cases the corresponding 4,5-dihydropyrroles were obtained in excellent yields (Table 3). Various haloaryl, especially fluoroaryl, substituted N-nosylaziridines were reacted efficiently with malononitrile to afford the corresponding

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CONCLUSION In conclusion, we have developed a very simple, efficient, and practical strategy for the synthesis of highly functionalized 4,5dihydropyrroles both in racemic as well as enantiopure forms via a LA catalyzed DROC of activated aziridines with malononitrile.

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EXPERIMENTAL SECTION

General Experimental. The progress of the reaction was monitored via thin layer chromatography (TLC) performed using silica gel 60 F254 precoated plates, and the spots were visualized using a UV lamp or I2 B

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Table 3. Scope of the Reaction with Various Substituted N-Nosyl Aziridines

a

Yields of isolated products after column chromatographic purification. C

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Table 4. Synthesis of Chiral 4,5-Dihydropyrroles

b

Yields of isolated products after column chromatographic purification. bee determined by chiral HPLC (see Supporting Information for details). Combined yield of both the regioisomers. dee could not be determined as the compound was obtained as an inseparable mixture of regioisomers (8:1). c

Table 5. Synthesis of Highly Substituted Chiral 4,5-Dihydropyrroles from 2,3-Disubstituted Chiral Aziridines

a

Yields of isolated products after column chromatographic purification.

Scheme 2. Synthesis of Highly Functionalized 4,5Dihydropyrroles

Figure 1. NOE experiment for the determination of stereochemistry of 3r. oven-dried glassware under nitrogen atmosphere using anhydrous solvents. Wherever appropriate, all reagents were purified prior to use following Perrin and Armarego guidelines.16 Monosubstituted N-Ns aziridines were synthesized according to a known literature report.17

stain. Silica gel 230−400 mesh size was used for flash column chromatography with a combination of ethyl acetate and petroleum ether as eluent. Unless otherwise noted, all reactions were carried out in D

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Scheme 3. Proposed Mechanism

found 340.1124. For (R)-3a: [α]25D = −35.1 (c 0.256, CHCl3); enantioselectivity of (R)-3a could not be determined as it is an inseparable mixture of regioisomers. 2-Amino-4-(3-chlorophenyl)-1-tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3b). The general method described above was followed when 1b (100 mg, 0.325 mmol) was reacted with malononitrile (31 μL, 0.487 mmol) in the presence of t-BuOK (55 mg, 0.487 mmol) using 20 mol % of Sc(OTf)3 (36 mg, 0.073 mmol) at 60 °C for 30 min to afford 3b (110 mg, 0.292 mmol) as a white frothy solid in 90% yield as a mixture of regioisomers (ratio 3:1): Rf 0.38 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3458, 3357, 2923, 2854, 2189, 1637, 1594, 1471, 1431, 1359, 1273, 1241, 1163, 1091, 1047, 809, 785, 743; 1H NMR of the major regioisomer (500 MHz, CDCl3) δ 2.49 (s, 3H), 3.49 (dd, J = 11.0, 4.9 Hz, 1H), 3.94 (dd, J = 10.4, 4.9 Hz, 1H), 4.14 (t, J = 10.4 Hz, 3H), 5.59 (s, 2H), 6.76−6.79 (m, 2H),7.09−7.26 (m, 3H), 7.36 (d, J = 8.0 Hz, 2H), 7.70 (d, J = 8.3 Hz, 2H); 13C NMR of the major regioisomer (125 MHz, CDCl3) δ 21.8, 42.5, 56.7, 63.5, 117.7, 126.8, 127.4, 127.7, 127.8, 130.3, 130.4, 132.6, 134.9, 144.0, 145.9, 155.3; HRMS (ESI) calcd for C18H16ClN3O2S (M − H)− 372.0574, found 372.0577. 2-Amino-1-(4-tert-butylphenylsulfonyl)-4-phenyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3c). The general method described above was followed when 1c (100 mg, 0.317 mmol) was reacted with malononitrile (30 μL, 0.476 mmol) in the presence of t-BuOK (53 mg, 0.476 mmol) using 20 mol % of Sc(OTf)3 (31 mg, 0.063 mmol) at 60 °C for 30 min to afford 3c (120 mg, 0.315 mmol) as a thick liquid in >99% yield as a mixture of regioisomers (ratio ∼4:1): Rf 0.38 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3447, 3365, 2964, 2870, 2190, 1647, 1592, 1470, 1427, 1358, 1264, 1199, 1167, 1113, 1085, 1045, 878, 799, 735, 700, 630; 1H NMR of the major regioisomer (400 MHz, CDCl3) δ 1.39 (s, 9H), 3.53 (dd, J = 10.8, 5.4 Hz, 1H), 3.99 (dd, J = 10.3, 5.4 Hz, 1H), 4.14 (t, J = 10.8 Hz, 3H), 5.66 (s, 2H), 6.83− 6.85 (m, 2H),7.14−7.28 (m, 3H), 7.58 (d, J = 8.8 Hz, 2H), 7.77 (d, J = 8.8 Hz, 2H); 13C NMR of the major regioisomer (125 MHz, CDCl3) δ 31.1, 35.5, 42.7, 56.9, 65.7, 118.1, 126.8, 126.9, 127.6, 127.8, 128.9, 132.6, 141.8, 155.1, 158.5; HRMS (ESI) calcd for C21H23N3O2S (M + H)+ 382.1589, found 382.1583. 2-Amino-4-isopropyl-1-tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3d). The general method described above was followed when 1d (100 mg, 0.418 mmol) was reacted with malononitrile (40 μL, 0.627 mmol) in the presence of t-BuOK (70 mg, 0.627 mmol) using 20 mol % of Sc(OTf)3 (41 mg, 0.084 mmol) at 60 °C for 30 min to afford 3d (118 mg, 0.386 mmol) as a white solid in 92% yield; mp 142−144 °C; Rf 0.41 (20% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3459, 3364, 2961, 2925, 2854, 2190, 1729, 1650, 1596, 1463, 1421, 1359, 1294, 1264, 1188, 1166, 1089, 1022, 873, 814, 735, 706, 666; 1H NMR (400 MHz, CDCl3) δ 0.90−0.92 (m, 6H), 2.15−2.31 (m, 3H), 2.47 (s, 3H), 3.81−3.86 (m, 1H), 5.38 (s, 2H), 7.36 (d, J = 7.8 Hz, 2H), 7.71 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 15.3, 18.2, 21.8, 26.8, 32.9, 61.5, 66.5, 118.4, 127.4, 130.3, 134.0, 145.3, 154.8; HRMS (ESI) calcd for C15H19N3O2S (M + H)+ 306.1276, found 306.1275. For (R)-3d [α]25D = +159.3 (c 0.203, CHCl3); er >99:1, enantiomeric ratio was determined by chiral HPLC analysis (Chiralpak AS-H column), hexane−isoproanol 95:5, flow rate = 1.0 mL/min; tR = 51.50 min.

Scheme 4. Denosylation of 4,5-Dihydropyrrole

Monosubstituted N-Ts aziridines18 and disubstituted aziridines8b were prepared from the corresponding amino alcohols following earlier reports. All commercial reagents were used as received without further purification unless mentioned. 1H NMR spectra were recorded on 400 or 500 MHz instruments, and the chemical shifts were recorded in parts per million (ppm, δ) taking tetramethyl silane (δ 0.00) as the internal standard. Splitting patterns of 1H NMR are designated as singlet (s), doublet (d), doublet of doublet (dd), triplet (t), quartet (q), multiplet (m), etc. 13C NMR spectra were recorded on 100 or 125 MHz instruments. HRMS were obtained using (ESI) mass spectrometer (TOF). IR spectra of liquid compounds were recorded as neat, whereas KBr plates were used for solid compounds. Melting points were measured using hot stage apparatus and are uncorrected. Enantiomeric excess (ee) was determined by HPLC using Chiralpak AS-H and Chiralcel OD-H columns (detection at 254 nm). Optical rotations were measured using a 6.0 mL cell with a 1.0 dm path length and are reported as [α]25D (c in g per 100 mL solvent) at 25 °C. Experimental Procedure. To a suspension of t-BuOK (1.5 equiv) in THF (2.0 mL) was added malononitrile (1.5 equiv) was added at room temperature under nitrogen atmosphere. Subsequently solutions of N-sulfonyl aziridine (100 mg, 1.0 equiv) and Sc(OTf)3 (20 mol %) in THF were added to the reaction mixture. Then the reaction mixture was stirred at 60 °C for the appropriate time. After complete consumption of the starting material (monitored by TLC), the reaction was quenched with saturated aqueous NH4Cl solution (1.0 mL). After separating the organic phase, the aqueous phase was extracted with ethyl acetate (3 × 1.0 mL), and the combined organic extracts were washed with brine and dried over anhydrous Na2SO4. After removal of the solvent under reduced pressure, the crude reaction mixture was purified by flash column chromatography on silica gel (230−400 mesh) using ethyl acetate in petroleum ether as the eluent to give pure 4,5dihydropyrroles. Spectral Data. 2-Amino-4-phenyl-1-tosyl-4,5-dihydro-1Hpyrrole-3-carbonitrile (3a). The general method described above was followed when 1a (100 mg, 0.366 mmol) was reacted with malononitrile (35 μL, 0.549 mmol) in the presence of t-BuOK (62 mg, 0.549 mmol) using 20 mol % of Sc(OTf)3 (36 mg, 0.073 mmol) at 60 °C for 30 min to afford 3a (120 mg, 0.354 mmol) as a white frothy solid in 97% yield as a mixture of regioisomers (ratio 8:1): Rf 0.44 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3448, 3362, 2963, 2190, 1646, 1594, 1469, 1454, 1425, 1355, 1276, 1164, 1088, 1043, 814, 770, 733; 1H NMR (500 MHz, CDCl3) δ 2.48 (s, 3H), 3.52 (dd, J = 10.7, 5.2 Hz, 1H), 3.97 (dd, J = 10.1, 5.2 Hz, 1H), 4.11 (t, J = 10.4 Hz, 3H), 5.67 (s, 2H), 6.83−6.86 (m, 2H), 7.14−7.18 (m, 3H), 7.35 (d, J = 8.3 Hz, 2H), 7.71 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.8, 42.8, 56.9, 65.7, 118.0, 126.9, 127.5, 127.8, 128.9, 130.4, 132.7, 141.7, 145.6, 155.1; HRMS (ESI) calcd for C18H17N3O2S (M + H)+ 340.1120, E

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The Journal of Organic Chemistry

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2-Amino-5-octyl-1-tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3e). The general method described above was followed when 1e (100 mg, 0.323 mmol) was reacted with malononitrile (31 μL, 0.485 mmol) in the presence of t-BuOK (54 mg, 0.485 mmol) using 20 mol % of Sc(OTf)3 (32 mg, 0.065 mmol) at 60 °C for 1.0 h to afford 3e (120 mg, 0.320 mmol) as a white solid in 99% yield; mp 80−82 °C; Rf 0.43 (20% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3443, 3347, 2925, 2854, 2188, 1649, 1604, 1465, 1411, 1347, 1305, 1162, 1088, 1020, 990, 813, 707, 663, 592; 1H NMR (400 MHz, CDCl3) δ 0.89 (t, J = 6.8 Hz, 3H), 1.28−1.81 (m, 14H), 2.13 (dd, J = 13.2, 2.9 Hz, 1H), 2.42− 2.48 (m, 1H), 2.47 (s, 3H), 3.89−3.95 (m, 1H), 5.38 (s, 2H), 7.36 (d, J = 8.3 Hz, 2H), 7.71 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 14.2, 21.8, 22.8, 24.4, 29.3, 29.5, 29.6, 31.2, 31.9, 36.6, 60.5, 62.0, 118.6, 127.3, 130.3, 134.2, 145.2, 154.4; HRMS (ESI) calcd for C20H29N3O2S (M + H)+ 376.2059, found 376.2057. 2-Amino-1-tosyl-3a,4,5,6,7,7a-hexahydro-1H-indole-3-carbonitrile (3f). The general method described above was followed when 1f (100 mg, 0.398 mmol) was reacted with malononitrile (38 μL, 0.597 mmol) in the presence of t-BuOK (67 mg, 0.597 mmol) using 20 mol % of Sc(OTf)3 (39 mg, 0.079 mmol) at 60 °C for 30 min to afford 3f (95 mg, 0.299 mmol) as a white solid in 75% yield; mp 152−154 °C; Rf 0.40 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3444, 3359, 3243, 3194, 2937, 2861, 2186, 1636, 1581, 1494, 1447, 1415, 1368, 1307, 1274, 1230, 1213, 1188, 1166, 1140, 1122, 1089, 1042, 1019, 967, 887, 835, 814, 779, 765, 736, 706, 662, 584; 1H NMR (400 MHz, CDCl3) δ 0.98−1.09 (m, 1H), 1.17−1.30 (m, 2H), 1.63−1.73 (m, 2H), 1.86−1.89 (m, 2H), 2.00−2.05 (m, 1H), 2.37−2.60 (m, 2H), 2.48 (s, 3H), 5.70 (s, 2H), 7.39 (d, J = 8.3 Hz, 2H), 7.70 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.8, 24.9, 25.0, 29.1, 30.7, 45.2, 65.5, 70.7, 118.1, 127.9, 130.3, 134.3, 145.5, 157.0; HRMS (ESI) calcd for C16H19N3O2S (M + H)+ 318.1276, found 318.1277. 2-Amino-1-(4-nitrophenylsulfonyl)-4-phenyl-4,5-dihydro1H-pyrrole-3-carbonitrile (3g). The general method described above was followed when 1g (100 mg, 0.329 mmol) was reacted with malononitrile (31 μL, 0.493 mmol) in the presence of t-BuOK (55 mg, 0.493 mmol) using 20 mol % of Sc(OTf)3 (32 mg, 0.066 mmol) at 60 °C for 5 min to afford 3g (107 mg, 0.289 mmol) as a yellow solid in 88% yield; color changes to brown at 150 °C; Rf 0.41 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3450, 3321, 3266, 3219, 3108, 2924, 2193, 1651, 1595, 1532, 1496, 1457, 1423, 1404, 1349, 1308, 1226, 1174, 1088, 964, 887, 856, 775, 762, 738, 702, 682, 645, 616, 597; 1 H NMR (400 MHz, CDCl3) δ 3.61 (dd, J = 10.7, 4.4 Hz, 1H), 4.00 (dd, J = 9.8, 4.4 Hz, 1H), 4.22 (dd, J = 11.2, 9.8 Hz, 1H), 5.64 (s, 2H), 6.85 (d, J = 6.4 Hz, 2H), 7.13−7.22 (m, 3H), 7.98 (d, J = 9.3 Hz, 2H), 8.33 (d, J = 8.8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 42.7, 57.5, 66.6, 117.2, 124.8, 126.6, 127.8, 128.9, 129.0, 141.3, 141.5, 151.0, 154.2; HRMS (ESI) calcd for C17H14N4O4S (M + H)+ 371.0814, found 371.0815. For (R)-3g [α]25D = +10.8 (c 0.425, CHCl3); er >99:1, enantiomeric ratio was determined by chiral HPLC analysis (Chiralcel OD-H column), hexane−isoproanol 90:10, flow rate = 1.0 mL/min; tR = 66.75 min. 2-Amino-4-(4-chlorophenyl)-1-(4-nitrophenylsulfonyl)-4,5dihydro-1H-pyrrole-3-carbonitrile (3h). The general method described above was followed when 1h (100 mg, 0.295 mmol) was reacted with malononitrile (28 μL, 0.443 mmol) in the presence of tBuOK (50 mg, 0.443 mmol) using 20 mol % of Sc(OTf)3 (29 mg, 0.059 mmol) at 60 °C for 5 min to afford 3h (102 mg, 0.252 mmol) as a yellow solid in 85% yield; color changes to brown at 152 °C; Rf 0.37 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3424, 3327, 3216, 2922, 2192, 1662, 1606, 1534, 1490, 1468, 1429, 1402, 1365, 1346, 1313, 1277, 1163, 1086, 1052, 1012, 853, 819, 783, 753, 739, 680, 654, 615, 580; 1H NMR (400 MHz, CDCl3) δ 3.57 (dd, J = 10.8, 4.9 Hz, 1H), 3.99 (dd, J = 9.8, 4.9 Hz, 1H), 4.17 (dd, J = 10.3, 10.5 Hz, 1H), 5.65 (s, 2H), 6.86 (d, J = 8.5 Hz, 2H), 7.17 (d, J = 8.3 Hz, 2H), 8.01 (d, J = 8.8 Hz, 2H), 8.39 (d, J = 8.8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 42.2, 57.2, 66.2, 117.0, 124.9, 128.1, 129.1, 129.3, 133.9, 139.6, 141.4, 151.0, 154.3; HRMS (ESI) calcd for C17H13ClN4O4S, (M + H)+ 405.0424, found 405.0421. 2-Amino-4-(3-chlorophenyl)-1-(4-nitrophenylsulfonyl)-4,5dihydro-1H-pyrrole-3-carbonitrile (3i). The general method

described above was followed when 1i (100 mg, 0.295 mmol) was reacted with malononitrile (28 μL, 0.443 mmol) in the presence of tBuOK (50 mg, 0.443 mmol) using 20 mol % of Sc(OTf)3 (29 mg, 0.059 mmol) at 60 °C for 5 min to afford 3i (106 mg, 0.262 mmol) as a yellow solid in 89% yield; color changes to brown at 192 °C; Rf 0.31 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3423, 3329, 3271, 3221, 2190, 1662, 1603, 1530, 1474, 1434, 1403, 1368, 1349, 1316, 1278, 1168, 1088, 1052, 1003, 854, 786, 755, 742, 681, 655, 622, 599, 573; 1H NMR (400 MHz, CDCl3) δ 3.59 (dd, J = 11.2, 3.9 Hz, 1H), 3.97 (m, 1H), 4.25 (dd, J = 11.0, 10.2 Hz, 1H), 5.64 (s, 2H), 6.59 (s, 1H), 6.83 (d, J = 7.3 Hz, 1H), 7.11−7.18 (m, 2H), 7.99 (d, J = 8.8 Hz, 2H), 8.38 (d, J = 9.0 Hz, 2H); 13C NMR (125 MHz, CDCl3+DMSO-d6) δ 42.1, 56.7, 63.4, 117.6, 124.6, 125.2, 126.1, 127.4, 128.8, 130.1, 134.2, 141.1, 144.3, 150.6, 154.5; HRMS (ESI) calcd for C17H13ClN4O4S (M + H)+ 405.0424, found 405.0423. 2-Amino-4-(4-bromophenyl)-1-(4-nitrophenylsulfonyl)-4,5dihydro-1H-pyrrole-3-carbonitrile (3j). The general method described above was followed when 1j (100 mg, 0.261 mmol) was reacted with malononitrile (25 μL, 0.391 mmol) in the presence of tBuOK (44 mg, 0.391 mmol) using 20 mol % of Sc(OTf)3 (26 mg, 0.052 mmol) at 60 °C for 5 min to afford 3j (100 mg, 0.222 mmol) as a yellow solid in 85% yield; starts blackening at 150 °C; Rf 0.31 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3424, 3327, 3267, 3216, 3097, 2924, 2854, 2192, 1663, 1606, 1532, 1487, 1467, 1429, 1402, 1365, 1345, 1313, 1291, 12276, 1176, 1163, 1109, 1085, 1051, 1008, 972, 853, 816, 777, 752, 739, 680, 654, 621, 610, 579, 557; 1H NMR (400 MHz, CDCl3) δ 3.57 (dd, J = 10.7, 4.9 Hz, 1H), 3.98 (dd, J = 9.8, 4.9 Hz, 1H), 4.17 (dd, J = 10.8, 10.0 Hz, 1H), 5.64 (s, 2H), 6.80 (d, J = 8.3 Hz, 2H), 7.33 (d, J = 8.3 Hz, 2H), 8.01 (d, J = 8.8 Hz, 2H), 8.39 (d, J = 8.8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 42.2, 57.1, 66.1, 117.0, 121.9, 124.9, 128.4, 129.0, 132.2, 140.2, 141.4, 151.0, 154.4; HRMS (ESI) calcd for C17H13BrN4O4S, (M − H)− 446.9763, found 446.9769. 2-Amino-4-(4-fluorophenyl)-1-(4-nitrophenylsulfonyl)-4,5dihydro-1H-pyrrole-3-carbonitrile (3k). The general method described above was followed when 1k (100 mg, 0.310 mmol) was reacted with malononitrile (29 μL, 0.465 mmol) in the presence of tBuOK (52 mg, 0.465 mmol) using 20 mol % of Sc(OTf)3 (31 mg, 0.062 mmol) at 60 °C for 5 min to afford 3k (105 mg, 0.271 mmol) as a yellow solid in 87% yield; melts to black liquid at 200 °C; Rf 0.30 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3442, 3321, 3264, 3209, 2195, 1660, 1606, 1532, 1508, 1468, 1433, 1403, 1361, 1349, 1317, 1277, 1226, 1164, 1086, 1052, 1012, 857, 837, 761, 737, 681, 618, 580; 1H NMR (400 MHz, CDCl3) δ 3.56 (dd, J = 10.5, 4.9 Hz, 1H), 4.01 (dd, J = 9.8, 5.1 Hz, 1H), 4.16 (dd, J = 10.5, 10.2 Hz, 1H), 5.61 (s, 2H), 6.89 (d, J = 6.6 Hz, 4H), 8.03 (d, J = 8.8 Hz, 2H), 8.40 (d, J = 9.0 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 42.1, 57.3, 66.7, 116.0, 116.1, 124.9, 128.3, 128.4, 129.1, 136.8(2C), 141.4, 151.0, 154.2, 161.3, 163.3, ; HRMS (ESI) calcd for C17H13FN4O4S, (M + H)+ 389.0720, found 389.0726. 2-Amino-1-(4-nitrophenylsulfonyl)-4-p-tolyl-4,5-dihydro1H-pyrrole-3-carbonitrile (3l). The general method described above was followed when 1l (100 mg, 0.314 mmol) was reacted with malononitrile (30 μL, 0.471 mmol) in the presence of t-BuOK (53 mg, 0.471 mmol) using 20 mol % of Sc(OTf)3 (31 mg, 0.063 mmol) at 60 °C for 5 min to afford 3l (107 mg, 0.278 mmol) as a yellow solid in 89% yield; starts blackening at 154 °C; Rf 0.37 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3426, 3329, 3271, 3220, 2924, 2191, 1665, 1606, 1529, 1470, 1429, 1367, 1347, 1314, 1281, 1177, 1088, 1054, 1007, 851, 809, 757, 740, 681, 619, 555 ; 1H NMR (400 MHz, CDCl3) δ 2.27 (s, 3H), 3.59 (dd, J = 10.8, 4.4 Hz, 1H), 3.96 (dd, J = 9.8, 4.4 Hz, 1H), 4.20 (dd, J = 10.5, 10.3 Hz, 1H), 5.59 (s, 2H), 6.72 (d, J = 7.8 Hz, 2H), 6.95 (d, J = 8.1 Hz, 2H), 7.97 (d, J = 8.8 Hz, 2H), 8.32 (d, J = 8.8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.0, 42.3, 57.7, 66.8, 117.3, 124.8, 126.4, 129.0, 129.7, 137.7, 138.3, 141.5, 150.9, 154.1; HRMS (ESI) calcd for C18H16N4O4S, (M + H)+ 385.0971, found 385.0974. 2-Amino-4-(4-tert-butylphenyl)-1-(4-nitrophenylsulfonyl)4,5-dihydro-1H-pyrrole-3-carbonitrile (3m). The general method described above was followed when 1m (100 mg, 0.277 mmol) was reacted with malononitrile (26 μL, 0.416 mmol) in the presence of tF

dx.doi.org/10.1021/jo302815m | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

3320, 3211, 2963, 2938, 2877, 2200, 1642, 1597, 1493, 1454, 1420, 1357, 1273, 1189, 1165, 1087, 1026, 993, 943, 884, 848, 809, 754, 728, 705, 662, 582; 1H NMR (500 MHz, CDCl3) δ 0.68 (t, J = 7.3 Hz, 3H), 0.99−1.05 (m, 2H), 1.24−1.27 (m, 1H), 1.45−1.55 (m, 1H), 2.49 (s, 3H), 3.89 (d, J = 8.6 Hz, 1H), 4.04−4.12 (m, 1H), 5.53 (s, 2H), 7.10 (d, J = 6.9 Hz, 2H), 7.23−7.30 (m, 3H), 7.41 (d, J = 8.3 Hz, 2H), 7.78 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 13.9, 18.9, 21.9, 33.5, 48.5, 66.4, 66.8, 118.1, 127.4, 127.9, 128.6, 128.9, 130.5, 134.4, 136.0, 145.5, 155.7; HRMS (ESI) calcd for C21H23N3O2S (M + H)+ 382.1589, found 382.1591. (4S,5S)-5-Allyl-2-amino-4-phenyl-1-tosyl-4,5-dihydro-1Hpyrrole-3-carbonitrile (3r). The general method described above was followed when 1r (100 mg, 0.319 mmol) was reacted with malononitrile (30 μL, 0.479 mmol) in the presence of t-BuOK (54 mg, 0.479 mmol) using 20 mol % of Sc(OTf)3 (31 mg, 0.064 mmol) at 60 °C for 2.0 h to afford 3r (121 mg, 0.318 mmol) as a white solid in >99% yield as a single diastereomer; mp 160−162 °C; Rf 0.45 (25% ethyl acetate in petroleum ether); [α]25D = +113.1 (c 0.175, CHCl3); IR νmax (KBr, cm−1) 3445, 3316, 2924, 2854, 2191, 1729, 1640, 1596, 1453, 1421, 1356, 1274, 1165, 1087, 1032, 995, 914, 889, 809, 749, 706, 667, 569; 1H NMR (500 MHz, CDCl3) δ 1.94−1.98 (m, 1H), 2.28−2.34 (m, 1H), 2.49 (s, 3H), 3.98 (d, J = 8.9 Hz, 1H), 4.13 (q, J = 6.7 Hz, 1H), 4.81 (d, J = 17.1 Hz, 1H), 4.90 (d, J = 10.1 Hz, 1H), 5.36−5.42 (m, 1H), 5.59 (s, 2H), 7.12 (d, J = 6.7 Hz, 2H), 7.25−7.30 (m, 3H), 7.41 (d, J = 8.3 Hz, 2H), 7.78 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.9, 36.1, 48.1, 66.0, 66.1, 117.9, 118.0, 127.4, 128.0, 128.6, 129.1, 130.5, 133.3, 134.4, 135.8, 145.6, 155.6; HRMS (ESI) calcd for C21H21N3O2S, (M + H)+ 380.1433, found 380.1430. 2-Amino-5-((tert-butyldimethylsilyloxy)methyl)-4-phenyl-1tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3s). The general method described above was followed when 1s (100 mg, 0.239 mmol) was reacted with malononitrile (23 μL, 0.359 mmol) in the presence of t-BuOK (40 mg, 0.359 mmol) using 20 mol % of Sc(OTf)3 (24 mg, 0.048 mmol) at 60 °C for 2.0 h to afford 3s (115 mg, 0.238 mmol) as a white solid in >99% yield as a single diastereomer; mp 166− 168 °C; Rf 0.41 (20% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3450, 3304, 3259, 3208, 2951, 2928, 2855, 2194, 1653, 1595, 1495, 1458, 1423, 1354, 1307, 1255, 1188, 1162, 1143, 1090, 1064, 1031, 1006, 912, 890, 839, 813, 780, 756, 704, 666, 600, 567; 1H NMR (500 MHz, CDCl3) δ −0.14 (s, 3H), −0.12 (s, 3H), 0.80 (s, 9H), 2.50 (s, 3H), 3.47−3.54 (m, 2H), 3.98−4.03 (m, 1H), 4.07 (d, J = 9.8 Hz, 1H), 5.56 (s, 2H), 7.19 (d, J = 6.6 Hz, 2H), 7.23−7.28 (m, 3H), 7.41 (d, J = 8.0 Hz, 2H), 7.78 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ −5.7, −5.6, 18.2, 21.8, 25.9, 47.1, 62.3, 66.3, 66.4, 118.0, 127.4, 127.7, 128.2, 129.4, 130.5, 134.2, 135.7, 145.5, 155.8; HRMS (ESI) calcd for C25H33N3O3SSi, (M + H)+ 484.2090, found 484.2094. Procedure for Denosylation of Compound 3g. Compound 3g (100 mg, 0.269 mmol) dissolved in CH3CN (4.0 mL) was added to a suspension of K2CO3 (149 mg, 1.076 mmol, 4.0 equiv) in CH3CN (4.7 mL), followed by addition of PhSH (83.0 μL, 0.809 mmol, 3.0 equiv) at room temperature under nitrogen atmosphere. Next DMSO (0.3 mL) was added to the reaction mixture, and stirring was continued at room temperature for 1 h. After complete consumption of the starting compound (monitored by TLC using 20% ethyl acetate in petroleum ether as the eluent), the reaction mixture was evaporated to give a pale yellow residue. The crude compound (the pale yellow residue) was purified by acid−base treatment as described below. Acid−Base Treatment. To the pale yellow residue were added water (5.0 mL) and diethyl ether (10.0 mL). After separating, the organic layer was washed with dilute NaHCO3 solution (3 × 2.0 mL). The organic layer was acidified with 5% HCl (5.0 mL). The aqueous layer was separated, and the organic layer was extracted with 5% HCl (2 × 5.0 mL). The combined aqueous extract was covered with a layer of diethyl ether (10.0 mL) and was made alkaline with aqueous 5 N NaOH solution (pH approximately 10) at 0 °C. The organic layer was separated, and the aqueous layer was extracted with diethyl ether (3 × 10.0 mL). The combined organic extract was washed with brine, dried over anhydrous Na2SO4, and evaporated to dryness to provide 4 in 80% yield (40 mg, 0.216 mmol) as a white solid in pure form as indicated by 1 H and 13C NMR and HRMS. Compound 4 was found to decompose

BuOK (47 mg, 0.416 mmol) using 20 mol % of Sc(OTf)3 (27 mg, 0.055 mmol) at 60 °C for 5 min to afford 3m (99 mg, 0.232 mmol) as a yellow solid in 84% yield; color changes to black at 124 °C; Rf 0.40 (25% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3436, 3325, 3265, 3211, 2962, 2926, 2869, 2193, 1664, 1605, 1531, 1464, 1430, 1402, 1366, 1348, 1315, 1271, 1166, 1087, 1050, 1013, 855, 833, 784, 754, 740, 681, 617, 587; 1H NMR (400 MHz, CDCl3) δ 1.25 (s, 9H), 3.59 (dd, J = 10.8, 4.6 Hz, 1H), 3.99 (dd, J = 9.8, 4.6 Hz, 1H), 4.19 (dd, J = 10.7, 10.0 Hz, 1H), 5.58 (s, 2H), 6.76 (d, J = 8.3 Hz, 2H), 7.16 (d, J = 8.3 Hz, 2H), 8.00 (d, J = 9.0 Hz, 2H), 8.36 (d, J = 8.8 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 31.3, 34.5, 42.2, 57.5, 66.9, 117.3, 124.8, 125.9, 126.2, 129.1, 138.0, 141.5, 150.9(2C), 154.1; HRMS (ESI) calcd for C21H22N4O4S, (M + H)+ 427.1440, found 427.1455. 2-Amino-4-(4-hydroxyphenyl)-1-(4-nitrophenylsulfonyl)4,5-dihydro-1H-pyrrole-3-carbonitrile (3n). The general method described above was followed when 1n (100 mg, 0.276 mmol) was reacted with malononitrile (26 μL, 0.414 mmol) in the presence of tBuOK (47 mg, 0.414 mmol) using 20 mol % of Sc(OTf)3 (27 mg, 0.055 mmol) at 60 °C for 5 min to afford 3n (94 mg, 0.243 mmol) as a yellow solid in 88% yield; blackens at 208 °C; Rf 0.31 (55% ethyl acetate in petroleum ether); IR νmax (KBr, cm−1) 3462, 3424, 3361, 3222, 3109, 2190, 1651, 1609, 1529, 1468, 1426, 1364, 1315, 1268, 1169, 1140, 1085, 1049, 1008, 855, 826, 760, 738, 681, 653; 1H NMR (500 MHz, CDCl3+DMSO-d6) δ 2.59−2.60 (m, 1H), 3.53 (dd, J = 11.0, 4.9 Hz, 1H), 3.90 (dd, J = 9.8, 4.6 Hz, 1H), 4.15 (dd, J = 10.7, 9.8 Hz, 1H), 6.42 (s, 2H), 6.60 (d, J = 8.6 Hz, 2H), 6.65 (d, J = 8.6 Hz, 2H), 8.02 (d, J = 8.9 Hz, 2H), 8.35 (d, J = 8.9 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 41.9, 57.6, 65.3, 115.6, 118.0, 124.6, 127.5, 129.0, 132.1, 141.5, 150.6, 154.1, 156.7; HRMS (ESI) calcd for C17H14N4O5S, (M + H)+ 387.0763, found 387.0760. (S)-2-Amino-4-benzyl-1-tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3o). The general method described above was followed when 1o (100 mg, 0.348 mmol) was reacted with malononitrile (33 μL, 0.522 mmol) in the presence of t-BuOK (59 mg, 0.522 mmol) using 20 mol % of Sc(OTf)3 (34 mg, 0.069 mmol) at 60 °C for 30 min to afford 3o (117 mg, 0.331 mmol) as a white solid in 95% yield; mp 141−143 °C; Rf 0.46 (25% ethyl acetate in petroleum ether); [α]25D = +156.9 (c 0.385, CHCl3); IR νmax (KBr, cm−1) 3454, 3364, 2924, 2854, 2190, 1730, 1648, 1595, 1495, 1454, 1425, 1359, 1294, 1266, 1165, 1089, 1034, 1004, 814, 738, 703, 664, 590, 548, 531; 1H NMR (500 MHz, CDCl3) δ 2.20−2.31 (m, 2H), 2.45 (s, 3H), 2.89 (dd, J = 13.5, 9.8 Hz, 1H), 3.24 (dd, J = 13.5, 3.7 Hz, 1H), 4.11−4.16 (m, 1H), 5.40 (s, 2H), 7.22−7.26 (m, 3H), 7.30−7.33 (m, 2H), 7.35 (d, J = 8.3 Hz, 2H), 7.74 (d, J = 8.3 Hz, 2H); 13 C NMR (125 MHz, CDCl3) δ 21.8, 30.1, 42.6, 59.9, 62.6, 118.4, 127.1, 127.3, 128.7, 129.7, 130.4, 134.3, 136.2, 145.4, 154.1; HRMS (ESI) calcd for C19H19N3O2S (M + H)+ 354.1276, found 354.1275. (S)-2-Amino-5-methyl-1-tosyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (3p). The general method described above was followed when 1p (100 mg, 0.473 mmol) was reacted with malononitrile (45 μL, 0.709 mmol) in the presence of t-BuOK (80 mg, 0.709 mmol) using 20 mol % of Sc(OTf)3 (47 mg, 0.095 mmol) at 60 °C for 30 min to afford 3p (121 mg, 0.436 mmol) as a white solid in 95% yield; mp 146−148 °C; Rf 0.46 (25% ethyl acetate in petroleum ether); [α]25D = +73.4 (c 0.515, CHCl3); IR νmax (KBr, cm−1) 3443, 3346, 2963, 2926, 2182, 1920, 1643, 1595, 1494, 1420, 1378, 1357, 1339, 1311, 1294, 1210, 1159, 1091, 1029, 890, 829, 813, 701, 680, 663, 626, 588; 1H NMR (400 MHz, CDCl3) δ 1.43 (d, J = 6.8 Hz, 3H), 2.06 (dd, J = 13.2, 3.4 Hz, 1H), 2.46 (s, 3H), 2.58 (dd, J = 13.2, 9.8 Hz, 1H), 3.98−4.06 (m, 1H), 5.48 (s, 2H), 7.36 (d, J = 7.8 Hz, 2H), 7.72 (d, J = 8.3 Hz, 2H); 13C NMR (125 MHz, CDCl3) δ 21.8, 23.6, 33.4, 57.9, 59.3, 118.7, 127.3, 130.3, 134.2, 145.3, 154.0; HRMS (ESI) calcd for C13H15N3O2S, (M + H)+ 278.0963, found 278.0967. (4S,5S)-2-Amino-4-phenyl-5-propyl-1-tosyl-4,5-dihydro-1Hpyrrole-3-carbonitrile (3q). The general method described above was followed when 1q (100 mg, 0.317 mmol) was reacted with malononitrile (30 μL, 0.476 mmol) in the presence of t-BuOK (53 mg, 0.476 mmol) using 20 mol % of Sc(OTf)3 (31 mg, 0.063 mmol) at 60 °C for 2.5 h to afford 3q (121 mg, 0.315 mmol) as a white solid in >99% yield as a single diastereomer; mp 140−142 °C; Rf 0.46 (25% ethyl acetate in petroleum ether); [α]25D = +52.8 (c 0.378, CHCl3); IR νmax (KBr, cm−1) 3452, G

dx.doi.org/10.1021/jo302815m | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

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Kimpe, N. Chem. Rev. 2007, 107, 2080. (e) Schneider, C. Angew. Chem., Int. Ed. 2009, 48, 2082. (f) Stanković, S.; D’hooghe, M.; Catak, S.; Eum, H.; Waroquier, M.; Speybroeck, V. V.; De Kimpe, N.; Ha, H.-J. Chem. Soc. Rev. 2012, 41, 643 and references therein. For some representative examples on aziridine chemistry see: (g) Enders, D.; Janeck, C. F.; Raabe, G. Eur. J. Org. Chem. 2000, 3337. (h) Vicario, J. L.; Badía, D.; Carrillo, L. J. Org. Chem. 2001, 66, 5801. (i) Cossy, J.; Bellosta, V.; Alauze, V.; Desmurs, J.-R. Synthesis 2002, 15, 2211. (j) Hale, K. J.; Domostoj, M. M.; Tocher, D. A.; Irving, E.; Scheinmann, F. Org. Lett. 2003, 5, 2927. (k) Forbeck, E. M.; Evans, C. D.; Gilleran, J. A.; Li, P.; Joullié, M. M. J. Am. Chem. Soc. 2007, 129, 14463. (l) Moss, T. A.; Fenwick, D. R.; Dixon, D. J. J. Am. Chem. Soc. 2008, 130, 10076. (m) Paixão, M. W.; Nielsen, M.; Jacobsen, C. B.; Jørgensen, K. A. Org. Biomol. Chem. 2008, 6, 3467. (n) Minakata, S.; Murakami, Y.; Satake, M.; Hidaka, I.; Okada, Y.; Komatsu, M. Org. Biomol. Chem. 2009, 7, 641. (o) Wu, B.; Gallucci, J. C.; Parquette, J. R.; RajanBabu, T. V. Angew. Chem., Int. Ed. 2009, 48, 1126. (p) Wu, B.; Parquette, J. R.; RajanBabu, T. V. Science 2009, 326, 1662. (q) Joullié, M. M.; Kelley, B. T. Org. Lett. 2010, 12, 4244. (r) Yadav, J. S.; Satheesh, G.; Murthy, C. V. S. R. Org. Lett. 2010, 12, 2544. (s) Ž ukauskaite, A.; Mangelinckx, S.; Buinauskaite, V.; Šačkus, A.; De Kimpe, N. Amino Acids 2011, 41, 541. (t) De Rycke, N.; David, O.; Couty, F. Org. Lett. 2011, 13, 1836. (u) D’hooghe, M.; Kenis, S.; Vervisch, K.; Lategan, C.; Smith, P. J.; Chibale, K.; De Kimpe, N. Eur. J. Med. Chem. 2011, 46, 579. (v) Bera, M.; Pratihar, S.; Roy, S. J. Org. Chem. 2011, 76, 1475. (w) Hajra, S.; Sinha, D. J. Org. Chem. 2011, 76, 7334. (x) Xu, Y.; Lin, L.; Kanai, M.; Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2011, 133, 5791. (y) Cockrell, J.; Wilhelmsen, C.; Rubin, H.; Martin, A.; Morgan, J. B. Angew. Chem., Int. Ed. 2012, 51, 9842. (z) De Vreese, R.; D’hooghe, M. Beilstein J. Org. Chem. 2012, 8, 398. (7) For synthesis of heterocyclic compounds from aziridines, see: (a) Karikomi, M.; D’hooghe, M.; Verniest, G.; De Kimpe, N. Org. Biomol. Chem. 2008, 6, 1902. (b) Ochoa-Terán, A.; Concellón, J. M.; Rivero, I. A. ARKIVOC 2009, No. ii, 288. (c) D’hooghe, M.; Van Nieuwenhove, A.; Van Brabandt, W.; Rottiers, M.; De Kimpe, N. Tetrahedron 2008, 64, 1064. (d) Zeng, F.; Alper, H. Org. Lett. 2010, 12, 5567. (e) Bhadra, S.; Adak, L.; Samanta, S.; Islam, A. K. M. M.; Mukherjee, M.; Ranu, B. C. J. Org. Chem. 2010, 75, 8533. (f) Druais, V.; Meyer, C.; Cossy, J. Org. Lett. 2012, 14, 516. (g) Baktharaman, S.; Afagh, N.; Vandersteen, A.; Yudin, A. K. Org. Lett. 2010, 12, 240. (h) Vervisch, K.; D’hooghe, M.; Törnroos, K. W.; De Kimpe, N. Org. Biomol. Chem. 2012, 10, 3308. (i) Prasad, D. J. C.; Sekar, G. Org. Biomol. Chem. 2009, 7, 5091. (j) Bisol, T. B.; Bortoluzzi, A. J.; Sá, M. M. J. Org. Chem. 2011, 76, 948. (k) Wu, Y.-C.; Zhu, J. Org. Lett. 2009, 11, 5558. (l) Du, X.; Yang, S.; Yang, J.; Liu, Y. Chem.Eur. J. 2011, 17, 4981. (8) (a) Ghorai, M. K.; Tiwari, D. P. J. Org. Chem. 2010, 75, 6173. (b) Ghorai, M. K.; Kumar, A.; Tiwari, D. P. J. Org. Chem. 2010, 75, 137. (c) Ghorai, M. K.; Shukla, D.; Das, K. J. Org. Chem. 2009, 74, 7013. (d) Ghorai, M. K.; Ghosh, K. Tetrahedron Lett. 2007, 48, 3191. (e) Ghorai, M. K.; Nanaji, Y.; Yadav, A. K. Org. Lett. 2011, 13, 4256. (f) Ghorai, M. K.; Sahoo, A. K.; Kumar, S. Org. Lett. 2011, 13, 4256. (g) Ghorai, M. K.; Shukla, D.; Bhattacharyya, A. J. Org. Chem. 2012, 77, 3740. (h) Ghorai, M. K.; Tiwari, D. P. Process for Preparation Chiral γLactams Indian Patent, 1870/DEL/2010, August 10, 2012. (9) For racemic 4,5-dihydropyrroles, see: (a) Sonoda, M.; Kuriyama, N.; Tomioka, Y.; Yamazaki, M. Chem. Pharm. Bull. 1982, 30, 2357. (b) Buchholz, B.; Stamm, H. Chem. Ber. 1987, 120, 1239. (c) Bouayad, Z.; Chanet-Ray, J.; Ducher, S.; Vessière, R. J. Heterocycl. Chem. 1991, 28, 1757. (10) For racemic 2,3-dihydropyrrole from aziridines, see: (a) Wender, P. A.; Strand, D. J. Am. Chem. Soc. 2009, 131, 7528. (b) Madhushaw, R. J.; Hu, C.-C.; Liu, R.-S. Org. Lett. 2002, 4, 4151. (c) Fan, J.; Gao, L.; Wang, Z. Chem. Commun. 2009, 5021. (11) (a) Ramiz, M. M. M.; Abdel, H.; Ibrahim, S.; Elian, M. A. J. Chin. Chem. Soc. 2012, 59, 758. (b) Huang, X.-G.; Liu, J.; Ren, J.; Wang, T.; Chen, W.; Zeng, B.-B. Tetrahedron 2011, 67, 6202. (c) Gopinath, P.; Chandrasekaran, S. J. Org. Chem. 2011, 76, 700. (d) Revelant, G.; Dunand, S.; Hesse, S.; Kirsch, G. Synthesis 2011, 2935. (12) Maligres, P. E.; See, M. M.; Askin, D.; Reider, P. J. Tetrahedron Lett. 1997, 38, 5253.

slowly at room temperature and upon exposure to light and/or air. However, it can be stored under Ar at lower temperature (−20 °C). 2-Amino-4-phenyl-4,5-dihydro-1H-pyrrole-3-carbonitrile (4). Rf 0.35 (10% methanol in chloroform); IR νmax (KBr, cm−1) 3418, 3342, 3373, 3258, 3222, 2922, 2887, 2156, 1654, 1639, 1591, 1509, 1468, 1450, 1343, 1312, 1204, 1155, 1071, 1028, 705, 767, 594, 551; 1H NMR (500 MHz, CDCl3) δ 3.57−3.68 (m, 1H), 3.68−3.76 (m, 1H), 3.77− 3.87 (m, 1H), 4.02−4.13 (m, 1H), 4.42−5.10 (m, 2H) 7.19−7.30 (m, 5H); 1H NMR (500 MHz, CDCl3 + D2O) δ 3.72 (dd, J = 13.7, 8.3 Hz, 1H), 3.88 (t, J = 8.0 Hz, 1H), 4.15 (dd, J = 13.8, 8.1 Hz, 1H), 4.71 (s, 1H), 7.23−7.38 (m, 5H); 13C NMR (125 MHz, CDCl3) δ 43.7, 50.9, 62.4, 116.4, 127.0, 128.0, 128.8, 129.2, 158.0; HRMS (ESI) calcd for C11H11N3, (M + H)+ 186.1031, found 186.1031.

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ASSOCIATED CONTENT

S Supporting Information *

NMR spectra for all the new compounds and HPLC chromatograms. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS M.K.G. is grateful to IIT-Kanpur and DST, India. D.P.T. thanks UGC and IIT Kanpur, India for a research fellowship. REFERENCES

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dx.doi.org/10.1021/jo302815m | J. Org. Chem. XXXX, XXX, XXX−XXX

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(13) Probably the other regioisomer if at all produced in the reaction was removed during column chromatography. There was no indication for the presence of the other regioisomer in the 1H NMR of the purified product. (14) (a) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc. Rev. 2008, 37, 320. (b) Müller, K.; Faeh, C.; Diederich, F. Science 2007, 317, 1881. (c) Anxionnat, B.; Robert, B.; George, P.; Ricci, G.; Perrin, M.-A.; Pardo, D. G.; Cossy, J. J. Org. Chem. 2012, 77, 6087. (15) See Supporting Information for spectra. (16) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.; Pergamon Press: Oxford, 1988. (17) Ryan, D.; McMorn, P.; Bethell, D.; Hutchings, G. Org. Biomol. Chem. 2004, 2, 3566. (18) Cernerud, M.; Adolfsson, H.; Moberg, C. Tetrahedron: Asymmetry 1997, 8, 2655.

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dx.doi.org/10.1021/jo302815m | J. Org. Chem. XXXX, XXX, XXX−XXX